Conventionally, an electronic watch has adopted, in order to reduce current consumption, a method in which a plurality of normal drive pulses are prepared and a normal drive pulse which enables driving with minimum energy is constantly selected therefrom to drive a motor. This selection method is briefly described. A normal drive pulse is first output and it is subsequently determined whether the motor has rotated. If the motor has not rotated, a correction drive pulse is immediately output to rotate a rotor reliably and, when a subsequent normal drive pulse is output, the normal drive pulse is switched to a normal drive pulse having the next higher-ranked driving power to the previous one and is then output. If the motor has rotated, on the other hand, the same normal drive pulse as the previous one is output when the next normal drive pulse is output. Then, when the same drive pulse is output a predetermined number of times, the drive pulse is switched to a normal drive pulse having the next lower-ranked driving power. The normal drive pulse has heretofore been selected by this method.
Note that the detection of whether the rotor has rotated or not in the conventional method often uses a method in which, after the application of a normal drive pulse is finished, a detection pulse is output to abruptly change the impedance value of a coil of a stepper motor, and an induced voltage generated in the coil is detected at the coil ends, to thereby determine the pattern of free oscillation of the rotor. For example, one of two drive inverters respectively connected to both the ends of the coil is first operated as a first detection mode to output a detection pulse, and when a rotation detection signal is generated, the first detection mode is stopped and the other drive inverter is operated as a second detection mode to output a detection pulse. When another rotation detection signal is generated in the second detection mode, it is determined that the rotation has succeeded.
The second detection mode detects that the rotation has succeeded, that is, the rotor has crossed over a magnetic potential hill. The detection in the first detection mode, on the other hand, is performed before the second detection mode in order to prevent detection of an erroneous detection signal which is generated before the rotor completely crosses over a magnetic potential hill when the rotor is relatively weakly driven. Specifically, the first detection mode prevents a current waveform c2 of FIG. 25, to be described later, from being erroneously detected as a signal exceeding the magnetic potential even though the rotation of the rotor is not finished. It is therefore known that performing the first detection before the second detection mode is a technology effective for performing more accurate rotation detection (see, for example, Patent Literatures 1 and 2).
Hereinafter, the conventional technology is described with reference to the drawings. FIG. 23 is a block diagram illustrating a circuit configuration of a conventional electronic watch. FIG. 24 are waveform diagrams of pulses that are generated by circuits of the conventional electronic watch. FIG. 25 are waveform diagrams of current and voltage that are generated in the coil when the rotor has succeeded in rotating. FIG. 26 are examples of waveform diagrams of current and voltage that are generated in the coil when the rotor has failed to rotate.
In FIG. 23, reference numeral 20 denotes a stepper motor including a coil 9 and a rotor 10; 1, an oscillation circuit; 2, a clock division circuit; and 3, a normal drive pulse generation circuit. As illustrated in FIG. 24(a), the normal drive pulse generation circuit 3 outputs a normal drive pulse SP every 0.5 ms in a width of 4 ms every second, on the second based on a signal of the clock division circuit 2. In this case, when a rotation detection signal of the rotor 10 is not generated and it is determined that the rotation has failed, the normal drive pulse SP is switched to a normal drive pulse SP2 having the next higher-ranked driving power to the previous one, as illustrated in FIG. 24(a), and is then output from the normal drive pulse generation circuit 3. Reference numeral 4 denotes a correction drive pulse generation circuit, which outputs a correction drive pulse FP of 7 ms as illustrated in FIG. 24(d) based on a signal of the clock division circuit 2. The correction drive pulse FP is output after 32 ms has elapsed from the second when the rotation detection signal of the rotor 10 is not generated and it is determined that the rotation has failed.
Reference numeral 5 denotes a first detection pulse generation circuit, which outputs detection pulses B5 to B12 to be used in the first detection mode based on a signal of the clock division circuit 2. As illustrated in FIG. 24(b), the detection pulses B5 to B12 are pulses each having a width of 0.125 ms and are output every 1 ms from 5 ms after the second until 12 ms has elapsed since the second. Reference numeral 6 denotes a second detection pulse generation circuit, which outputs detection pulses F7 to F14 to be used in the second detection mode based on a signal of the clock division circuit 2. As illustrated in FIG. 24(c), the detection pulses F7 to F14 are pulses each having a width of 0.125 ms and are output every 1 ms from 7 ms after the second until 14 ms has elapsed since the second.
Reference numeral 7 denotes a pulse selection circuit, which selects and outputs the signals output from the normal drive pulse generation circuit 3, the correction drive pulse generation circuit 4, the first detection pulse generation circuit 5, and the second detection pulse generation circuit 6 based on determination results of a first detection mode determination circuit 12 and a second detection mode determination circuit 13, to be described later. Reference numeral 8 denotes a driver circuit, which outputs a signal of the pulse selection circuit 7 to the coil 9 to rotationally drive the rotor 10 and also control the rotation detection. The driver circuit 8 outputs the respective pulses alternately from a terminal O1 and a terminal O2 every 1 second. The internal configuration of the driver circuit 8 is the same as in patent literatures to be described later (a drive circuit 17, detection resistors R1 and R2, and MOS transistors Tr1 and Tr2 in FIG. 1 of Patent Literature 1 and FIG. 1 of Patent Literature 2), and detailed description thereof is therefore omitted. Reference numeral 11 denotes a detection circuit, which detects an induced voltage generated in the coil 9. Reference numeral 12 denotes the first detection mode determination circuit for determining the first detection mode based on a detection signal of the detection circuit 11. Reference numeral 13 denotes the second detection mode determination circuit for determining the second detection mode based on a detection signal of the detection circuit 11.
Note that the detection pulses B5 to B12 are output to a terminal on the opposite side of a terminal to which the normal drive pulse SP is output, and hence the detection pulses B5 to B12 abruptly change the impedance of a closed loop including the coil 9 to amplify a counter-electromotive voltage that is generated by free oscillation of the rotor 10 after the application of the normal drive pulse SP. The amplified counter-electromotive voltage is then detected by the detection circuit 11. The detection pulses F7 to F14 are output to a terminal on the same side of the terminal to which the normal drive pulse SP is output, and hence the detection pulses F7 to F14 abruptly change the impedance of the closed loop including the coil 9 to amplify a counter-electromotive voltage that is generated by free oscillation of the rotor 10 after the application of the normal drive pulses SP. The amplified counter-electromotive voltage is then detected by the detection circuit 11.
Subsequently, the operation of the above-mentioned configuration is described. The pulse selection circuit 7 selects, on the second, the normal drive pulse SP output from the normal drive pulse generation circuit 3 and drives the stepper motor 20. After 5 ms from the second, the first detection mode is started. In the first detection mode, the pulse selection circuit 7 selects and outputs the detection pulses B5 to B12 output from the first detection pulse generation circuit 5, and controls the stepper motor 20 so as to change the impedance of the coil 9. The detection circuit 11 then detects induced voltages that are generated in the coil 9 by the detection pulses B5 to B12. The pulse selection circuit 7, on the other hand, instructs the first detection mode determination circuit 12 to start its determination operation. The first detection mode determination circuit 12 determines the presence or absence of the detection signal in the first detection mode based on the number of times the detection signal is input from the detection circuit 11. When the detection signal of the detection circuit 11 has been generated twice, the first detection mode determination circuit 12 determines the detection and immediately stops the detection pulses output from the first detection pulse generation circuit 5 to notify the pulse selection circuit 7 so as to end the operation of the first detection mode. The first detection mode determination circuit 12 further instructs the second detection mode determination circuit 13 to start its operation, to thereby shift to the second detection mode. However, when the detection pulses B5 to B12 have produced no detection signal at all, or only one detection signal, the first detection mode determination circuit 12 determines that the rotation has failed and ends the operation of the first detection mode. Then, without shifting to the second detection mode, the correction drive pulse FP is output, and when the next normal drive pulse is output, the normal drive pulse SP2 having the next higher-ranked driving power to the previous one is output from the normal drive pulse generation circuit 3.
In the second detection mode, the pulse selection circuit 7 selects and outputs the detection pulses F7 to F14 generated by the second detection pulse generation circuit 6, and controls the stepper motor 20. The detection circuit 11 then detects induced voltages that are generated in the coil 9 by the detection pulses F7 to F14. The second detection mode determination circuit 13 receives the detection signal of the detection circuit 11. When the detection signal has been generated twice, the second detection mode determination circuit 13 determines that the rotation has succeeded and immediately stops the detection pulses output from the second detection pulse generation circuit 6 to end the operation of the second detection mode, and further controls the pulse selection circuit 7 so as not to output the correction drive pulse FP. However, the detection of the detection signals generated by the detection pulses F7 to F14 is finished when the detection signal has been detected six times at most. If no detection signal, or only one detection signal, is generated during the detection, it is determined that the rotation has failed and the correction drive pulse FP is output. Then, when the next normal drive pulse is output, the normal drive pulse SP2 having the next higher-ranked driving power to the previous one is output from the normal drive pulse generation circuit 3.
An actual method of detecting the rotation through the above-mentioned operation is described with reference to the waveform diagrams of FIGS. 25 and 24. First, the case where the rotor 10 has rotated normally is described. FIG. 25(a) is a waveform of a current that is induced in the coil 9 when the rotor 10 rotates. FIG. 25(b) is a waveform of a voltage generated at one terminal O1 of the coil 9 in the second detection mode. FIG. 25(c) is a waveform of a voltage generated at another terminal O2 of the coil 9 in the first detection mode. Note that the waveforms generated at the terminals O1 and O2 are alternating pulses whose phases are inverted every 1 second.
First, the normal drive pulse SP illustrated in FIG. 24(a) is applied to the terminal O1 of the coil 9, and the rotor 10 rotates. The current waveform at this time is a waveform c1 of FIG. 25(a). After the end of the normal drive pulse SP, the rotor 10 becomes a freely oscillated state, and the current waveform becomes induced current waveforms denoted by c2, c3, and c4. At a time of 5 ms, the first detection mode is started, and the detection pulse B5 illustrated in FIG. 24(b) is applied to the coil 9. As illustrated in FIG. 25(a), at 5 ms, the current waveform is in the region of the current waveform c2, in which the current value is negative. Accordingly, as illustrated in FIG. 25(c), an induced voltage V5 generated by the detection pulse B5 never exceeds a threshold Vth of the detection circuit (hereinafter, simply referred to as threshold Vth). At 7 ms, however, the current waveform is in the region of the current waveform c3, in which the current value is changed to the positive direction. Accordingly, as illustrated in FIG. 25(c), an induced voltage V7 generated by the detection pulse B7 becomes a detection signal exceeding the threshold Vth. Similarly at 8 ms, the current waveform is also in the region of the current waveform c3, and an induced voltage V8 generated by the detection pulse B8 becomes a detection signal exceeding the threshold Vth. Because the two detection signals of the induced voltages V7 and V8 have exceeded the threshold Vth, the mode is switched to the second detection mode.
In response to the switching to the second detection mode by the induced voltage V8, a next timing detection pulse, namely the detection pulse F9 at the time of 9 ms illustrated in FIG. 24(c), is applied to the coil 9. As illustrated in FIG. 25(a), at 9 ms, the current waveform is in the region of the current waveform c3, in which the current value is positive, and hence, as illustrated in FIG. 25(b), an induced voltage V9 generated by the detection pulse F9 never exceeds the threshold Vth. Further, the current waveform for an induced voltage V10 generated by the detection pulse F10 is also in the region of the current waveform c3, and hence the induced voltage V10 never exceeds the threshold Vth. At 11 ms, however, as illustrated in FIG. 25(a), the current waveform is in the region of the current waveform c4, in which the current value is changed to the negative direction, and, as illustrated in FIG. 25(b), induced voltages V11 and V12 generated by the detection pulses F11 and F12 become detection signals exceeding the threshold Vth. Because the two detection signals of the induced voltages V11 and V12 have exceeded the threshold Vth, the second detection mode determination circuit 13 determines that the rotation has succeeded. Then, the correction drive pulse FP is not output, and when the next normal drive pulse is output, the normal drive pulse SP having the same driving power as the previous one is output.
Subsequently, the case where the rotor 10 has failed to rotate is described with reference to the waveform diagrams of FIGS. 26 and 24. FIG. 26(a) is a waveform of a current that is induced in the coil 9 when the rotor 10 has failed to rotate because, for example, the operating voltage of the driver circuit 8 has reduced to lower the driving power of the stepper motor 20. FIG. 26(b) is a waveform of a voltage generated at one terminal O1 of the coil 9 at this time, and FIG. 26(c) is a waveform of a voltage generated at another terminal O2 of the coil 9.
The waveform of the current that is generated in the coil when the rotation has failed is the current waveform as illustrated in FIG. 26(a). That is, up to the current waveform c1, the current exhibits substantially the same current waveform as that in the above-mentioned case where the rotation has succeeded, but subsequently exhibits current waveforms c2, c5, and c6. The waveform of the current that is generated in the coil 9 when the rotation has failed is longer and more gentle, as illustrated by the current waveform c5, than the current waveform in the case where the rotation has succeeded. The same method of detecting the rotation is also applied in the case where the rotation has failed. First, at the time of 5 ms, the first detection mode is started, and the detection pulse B5 is applied to the coil 9. As illustrated in FIG. 26(a), at 5 ms, the current waveform is in the region of the current waveform c2, in which the current value is negative. Accordingly, as illustrated in FIG. 26(c), the induced voltage V5 never exceeds the threshold Vth. At 8 ms, however, the current waveform is in the region of the current waveform c5, in which the current value is changed to the positive direction. Accordingly, as illustrated in FIG. 26(c), the induced voltage V8 becomes a detection signal exceeding the threshold Vth. Similarly at 9 ms, the current waveform is also in the region of the current waveform c5, and the induced voltage V9 becomes a detection signal exceeding the threshold Vth. Because the two detection signals of the induced voltages V8 and V9 have exceeded the threshold Vth, the mode is switched to the second detection mode.
In response to the switching to the second detection mode by the induced voltage V9, a next timing detection pulse, namely the detection pulse F10 at the timing of 10 ms illustrated in FIG. 24(c), is applied to the coil 9. As illustrated in FIG. 26(a), at 10 ms, the current waveform is in the region of the current waveform c5, in which the current value is positive. Accordingly, as illustrated in FIG. 26(b), the induced voltage V10 never exceeds the threshold Vth. Further, the current waveform for the induced voltages V10 to V14 generated by the detection pulses F10 to F14 is also in the region of the current waveform c5. It follows that no detection signal exceeding the threshold is detected within detection periods from the induced voltage V10 to the induced voltage V14. The second detection mode determination circuit 13 therefore determines that the rotation has failed and terminates the determination, with the result that the pulse selection circuit 7 selects the correction drive pulse FP to drive the stepper motor 20 so that the rotor 10 is reliably rotated. In this manner, the detection of whether the rotor has rotated or not is performed and, if the rotation has failed, the correction drive pulse FP can be output as appropriate so that the normal drive pulse SP2 having the next higher-ranked driving power to the previous one can be output when a next normal drive pulse is output.
As described above, in the case where the stepper motor 20 does not rotate normally, the correction drive pulse having sufficiently large effective electric power is output so as to reliably rotate the stepper motor 20 and increase the effective electric power of the normal drive pulse. Thus, the stepper motor 20 can be driven with the lowest electric power possible.
However, the above-mentioned technology can sometimes not perform detection well because of current waveform disturbance in the case where an indicating hand having a large moment of inertia is used. This problem is described with reference to waveform diagrams of FIGS. 27 and 24. FIG. 27 are waveform diagrams of current and voltage that are generated when the rotor 10 rotates in the case where an indicating hand having a large moment of inertia is attached to the conventional electronic watch. FIG. 27(a) is a waveform of a current that is induced in the coil 9 when the indicating hand having a large moment of inertia is attached. FIG. 27(b) is a waveform of a voltage generated at one terminal O1 of the coil 9 at this time, and FIG. 27(c) is a waveform of a voltage generated at another terminal O2 of the coil 9.
In the case where an indicating hand having a large moment of inertia is attached to a general drive circuit, the current waveform is as illustrated in FIG. 27(a). That is, the waveform profile exhibits induced current waveforms c2, c3, and c4 followed by a current waveform c1. Compared with the current waveform illustrated in FIG. 25(a), the period of the current waveform c3 is long and the current waveform c4 is flattened. This is because the free oscillation of the rotor 10 is restricted by the moment of inertia of the indicating hand. Hereinafter, the detection operation in this case is described. First, at 5 ms, the first detection mode is started, and the detection pulse B5 is applied to the coil 9. As illustrated in FIG. 27(a), at 6 ms, the current waveform is in the region of the current waveform c2, in which the current value is negative. Accordingly, as illustrated in FIG. 27(c), the induced voltage V6 never exceeds the threshold Vth. At 7 ms, however, the current waveform is in the region of the current waveform c3, in which the current value is changed to the positive direction. Accordingly, as illustrated in FIG. 27(c), the induced voltage V7 becomes a detection signal exceeding the threshold Vth. Similarly at 8 ms, the current waveform is also in the region of the current waveform c3, and the induced voltage V8 becomes a detection signal exceeding the threshold Vth. Because the two detection signals of the induced voltages V7 and V8 have exceeded the threshold Vth, the mode is switched to the second detection mode.
In response to the switching to the second detection mode by the induced voltage V8, the next timing detection pulse, namely the detection pulse F9 at the time of 9 ms, is applied to the coil 9. As illustrated in FIG. 27(a), at 9 ms, the current waveform is in the region of the current waveform c3, in which the current value is positive. Accordingly, as illustrated in FIG. 27(b), the induced voltage V9 never exceeds the threshold Vth. Similarly, the current waveform for the induced voltages V10 and V11 is also in the region of the current waveform c3, and hence the induced voltages V10 and V11 never exceed the threshold Vth. At 12 ms, the current waveform is in the region of the current waveform c4, in which the current value is changed to the negative direction. Accordingly, as illustrated in FIG. 27(b), an induced voltage V12 generated by the detection pulse F12 becomes a detection signal exceeding the threshold Vth. At 13 ms, however, the current waveform is in the region of the current waveform c4, in which the current value is negative, but because the current waveform is disturbed by the influence of the indicating hand having a large moment of inertia, an induced voltage exceeding the threshold Vth cannot be obtained from an induced voltage V13 generated by the detection pulse F13. Further, an induced voltage V14 generated by the detection pulse F14 is outside the region of the current waveform c4 and hence never exceeds the threshold Vth. It follows that a detection signal exceeding the threshold is not detected twice within six detection periods from the induced voltage V9 to the induced voltage V14. Therefore, the second detection mode determination circuit 13 determines that the rotation has failed, and the pulse selection circuit 7 selects and outputs the correction drive pulse FP. In other words, this leads to a phenomenon that, even though the rotation has succeeded, the correction drive pulse FP is output due to such erroneous determination, and when the next normal drive pulse is output, the normal drive pulse SP2 having the next higher-ranked driving power to the previous one is output from the normal drive pulse generation circuit 3, with the result that unnecessary current consumption is increased. Thus, the battery life is significantly reduced.
Let us consider countermeasures of increasing the detection pulse width in order to solve the above-mentioned problem. The detection pulse described above serves to detect the rotation of the rotor 10 and also suppress the electromagnetic brake of the rotor. That is, when the detection pulse is output, the detection pulse abruptly changes the impedance value of the coil of the stepper motor and therefore sets the state of the closed loop including the coil 9 to the high impedance state.
Note that, in addition to the case where the terminals O1 and O2 are opened so that the closed loop may have high impedance, it is also conceivable to connect the detection resistors R1 and R2 to the opened terminals O1 and O2 as disclosed in page 2 of Patent Literature 2. The resistance values of the detection resistors R1 and R2 (at the level of 100 kΩ) are larger than the resistance value of the coil (several kΩ), and hence the same effects can be obtained as in the case of setting to high impedance. Herein, both the states are referred to as high impedance.
At the moment when the high impedance state is established, an induced voltage that is generated in the coil by free oscillation of the rotor 10 is detected, and the obtained detection signal is used to detect the rotation of the rotor 10. If the high impedance state is continued, there is no chance to generate such induced electromotive force as to generate a magnetic field in the direction of preventing the change of magnetic flux generated in the coil 9 by the free oscillation of the rotor 10, namely electromagnetic brake. It is therefore possible to permit rapid reduction in speed of the free oscillation of the rotor 10 to some extent.
Now, the case where the detection pulse width is increased is described with reference to waveform diagrams of FIGS. 28 and 29. FIG. 28 are waveform diagrams of current and voltage that are generated when the rotor 10 rotates in the case where the detection pulse width is changed from 0.125 ms to 0.25 ms and an indicating hand having a large moment of inertia is attached to the conventional electronic watch. FIG. 28(a) is a waveform of a current that is induced in the coil 9 when the indicating hand having a large moment of inertia is attached. FIG. 28(b) is a waveform of a voltage generated at one terminal O1 of the coil 9 at this time, and FIG. 28(c) is a waveform of a voltage generated at another terminal O2 of the coil 9.
In the case where an indicating hand having a large moment of inertia is attached to a general drive circuit and further the detection pulse width is changed from 0.125 ms to 0.25 ms, the current waveform is as illustrated in FIG. 28(a). That is, the waveform profile exhibits induced current waveforms c2, c3, and c4 followed by a current waveform c1. Compared with the current waveform illustrated in FIG. 27(a), the electromagnetic brake is suppressed to increase the free oscillation of the rotor 10 and the current waveform c4 expands. Hereinafter, the detection operation in this case is described. First, at the time of 5 ms, the first detection mode is started, and the detection pulse B5 is applied to the coil 9. As illustrated in FIG. 28(a), at 6 ms, the current waveform is in the region of the current waveform c2, in which the current value is negative. Accordingly, as illustrated in FIG. 27(c), the induced voltage V6 never exceeds the threshold Vth. At 7 ms, however, the current waveform is in the region of the current waveform c3, in which the current value is changed to the positive direction. Accordingly, as illustrated in FIG. 28(c), the induced voltage V7 becomes a detection signal exceeding the threshold Vth. Similarly at 8 ms, the current waveform is also in the region of the current waveform c3, and the induced voltage V8 becomes a detection signal exceeding the threshold Vth. Because the two detection signals of the induced voltages V7 and V8 have exceeded the threshold Vth, the mode is switched to the second detection mode.
In response to the switching to the second detection mode by the induced voltage V8, the next timing detection pulse, namely the detection pulse F9 at the time of 9 ms, is applied to the coil 9. As illustrated in FIG. 28(a), at 9 ms, the current waveform is in the region of the current waveform c3, in which the current value is positive. Accordingly, as illustrated in FIG. 28(b), the induced voltage V9 never exceeds the threshold Vth. Similarly, the current waveform for the induced voltages V10 and V11 is also in the region of the current waveform c3, and hence the induced voltages V10 and V11 never exceed the threshold Vth. At 12 ms, however, the current waveform is in the region of the current waveform c4, in which the current value is changed to the negative direction, and hence, as illustrated in FIG. 28(b), induced voltages V12 and V13 generated by the detection pulses F12 and F13 become detection signals exceeding the threshold Vth. Because the two detection signals of the induced voltages V12 and V13 have exceeded the threshold Vth, the second detection mode determination circuit 13 determines that the rotation has succeeded. Then, the correction drive pulse FP is not output, and when the next normal drive pulse is output, the normal drive pulse SP having the same driving power as the previous one is output. In other words, a phenomenon where unnecessary current consumption is increased never occurs, nor is the battery life significantly reduced.
Patent Literature 3 describes that the width of a detection pulse is variable and the width of the detection pulse concerned is adjusted in accordance with indicating hands having different moments of inertia in the manner described above, to thereby change the amount of braking.